`let constructor` is legacy (do not use in tree!) since the table gen
backend emits most of the glue logic to build a pass. This PR retires
the td method for Shape and MLProgram
Added pass optimizes MLProgram global operations by reducing to only
the minimal load/store operations for global tensors. This avoids
unnecessary global operations throughout a program and potentially
improves operation gusion.
Reviewed By: jpienaar
Differential Revision: https://reviews.llvm.org/D159228
